1. Field of the Invention
The present invention relates to the introduction of water into soil.
2. Description of Related Art
The long-term acceptance and infiltration of water into soil, earthen materials and other permeable media used for treatment (referred to collectively herein as soil) is a main component of all leaching systems. Leaching systems are utilized for general drainage applications such as with storm water (including irrigation drainage) treatment and disposal, and wastewater treatment and disposal systems. We collectively refer to all of these types of water sources as water. By the term leaching structure, we mean any device or combination of materials and devices that serve to facilitate the introduction of water into soil.
More commonly utilized leaching systems include a trench filled with gravel, a perforated pipe in the center, and filter fabric. We also refer to these components and combinations as leaching systems. Specific examples include the BioDiffuser Standard and High Capacity Chambers, manufactured by Advanced Drainage Systems/PSA, Hilliard, Ohio and Draincore 2, manufactured by Invisible Structures, Inc., Golden, Colo. Over time, the performance of all these infiltration systems generally diminishes.
This is especially problematic in situations where water, nutrients and organic matter are present; this often occurs in landscaped areas where plant fertilizers are utilized and in wastewater applications. This can occur even with parking lot drainage and others situations where organic compounds such as hydrocarbons are present. Under these conditions, the nutrients and organic matter dissolved and suspended in the water must flow through the soil/media infiltrative surface. The suspended organic matter is deposited on this interface and microorganisms flourish under these optimal conditions. This is often referred to as biomat. Over time the organic matter and microorganisms begin to diminish the hydraulic capacity and treatment efficiency of the constituents in the water.
In order to prevent premature leaching system failure, the maximum infiltration surface area is desirable. This has resulted in prior art leaching systems having relatively large penetrations through the sidewall. These penetrations are commonly about 0.25-0.50 inches high by approximately 1-4 inches long. These penetrations are typically larger on the soil interface side than they are on the inside of the leaching structure. The penetrations are intended to prevent the surrounding soil from intruding by having a so called “louver”, “eyebrow” or sloped shield above them, that is aimed at preventing soil from migrating and intruding into the void of the leaching system. One commercial product with this type of penetration is the Standard EnviroChamber manufactured by Hancor, Findlay, Ohio; another is the Standard Infiltrator Chamber, manufactured by Infiltrator Systems, Old Saybrook, Conn. and which is disclosed in U.S. Pat. No. 5,511,903, which is incorporated herein by reference thereto. Reportedly, the theory behind this sloped shield was that it served to negate the angle of repose of the surrounding soil, thus theoretically preventing the soil from intruding all the way into the interior of the structure. However, this theory only serves to work when the soil is cohesive and/or when dry and gravity is the predominant force. Unfortunately, the soil is frequently damp to saturated, since the intended use is to infiltrate water. This results in reduced friction between soil particles and a change in the angle of repose. Furthermore, when the soil pores are saturated, changes in water level within the leaching structure associated with use are directly transmitted through the saturated soil pores. Under these conditions, surface tension between the water in the soil pores and the soil particles can result in fluidization and flow of soil into the leaching system. This problem is exacerbated because the cross sectional area of the typical prior art sidewall perforations are typically larger on the leaching structure/soil interface side than on the interior of the leaching structure. This results in an increase in velocity as the soil moves into the structure. When the soil intrudes into the hollow leaching system, if unchecked and not designed accordingly, it can gradually fill the entire structure. When this occurs, the performance of the leaching system can be dramatically diminished, if not eliminated.
The prevention of soil intrusion into leaching systems has been addressed through the use of geotextile filter fabrics, such as #65304 geotextile fabric manufactured by Mirafi, Pendergrass, Ga. When placed in a manner such that water flows through this material, this often results in the fabric prematurely loosing hydraulic capacity. This is commonly caused by accumulations of organic matter and the subsequent microbial fouling of the filter fabric at the infiltrative surface interface. This becomes especially problematic when the fabric is placed between the leaching structure and the high permeability soil that is typically utilized or naturally occurring around leaching systems. In this situation the capillary forces present within the fabric are significantly greater than that which is present in the surrounding soil. This results in the retention of moisture in the fabric, and optimum conditions for proliferation by microorganisms. These microorganisms tend to produce slimy substances, such as polysaccharides, that further degrade the hydraulic conductivity of the filter fabric. This is especially problematic under anaerobic conditions.
Simple round or oblong holes (holes) and perforations have also met with only limited success. If the holes are too big they will affect the structural integrity of the leaching system and soil will likely intrude the structure. If they are too small, they will clog with organic matter in the water and be particularly susceptible to biological fouling. This is especially problematic when the surface tension present between the orifice and the soil is insufficient to draw the water from the orifice in the absence of head or tension. Often times leaching structures with holes are covered with gravel or filter fabric; but as discussed above, gravel is inconvenient and expensive and filter fabric can be problematic. An example of a prior art leaching structure is the Contactor 100 Chamber manufactured by Cultec, Brookfield, Conn. This product is typically used in conjunction with gravel or filter fabric and has oblong perforations in the sidewall.